What will the James Webb Space Telescope reveal about the newly discovered exoplanets?

The discovery of seven habitable planets just 40 light years away is certainly impressive, but the fact is, they are still 40 light years away. Unless we’re willing and able to spend thousands of years traveling through space, we won’t be rolling into the TRAPPIST-1 system anytime soon. This means that over the coming decades, advanced scientific instruments closer to home will play very important roles in exploring these distant worlds – perhaps none more so than the James Webb Space Telescope. So what can we expect when it is fired into orbit next year? We checked in with some of the scientists behind yesterday’s hugely exciting discovery to learn how astronomers will use NASA’s next-generation space telescope to probe the secrets of the TRAPPIST-1 system.

The James Webb Space Telescope (JWST) has been almost two decades in the making and, spanning the size of a tennis court, will be the largest space telescope ever assembled. Poised to take the reins from Hubble as NASA’s premier orbiting telescope in 2018, it will boast seven times the light-collecting capacity of its predecessor and will be sensitive enough to spot a single firefly one million kilometers away.

Astronomers plan to put its capabilities to use in a number of exciting ways, such as looking back over 13.5 billion years to unravel the mysteries of the early universe, exploring how early stars and galaxies formed, and studying the atmospheres of planets outside our solar system. But as Adam Burgasser, an astrophysicist at UC San Diego and co-author on yesterday’s groundbreaking paper tells us, the new discovery will place the TRAPPIST-1 system among its top science priorities.

“I suspect TRAPPIST-1 will be one of the first targets for the facility,” he says. “I know several of the scientists on the instrument teams. Those that helped build and test the cameras on the telescope are eager to flex their muscles on this exciting system, and of course we will be proposing to observe the sources as soon as we can.”

According to Katherine Deck, study co-author and research fellow at Caltech (the research institute behind NASA’s Jet Propulsion Laboratory), promptly pointing the JWST in the direction of TRAPPIST-1 makes a lot of sense.

“One major research priority for JWST is to characterize the atmospheres of Earth-sized planets, and Trappist-1, with six Earth-sized planets – three of which are in the nominal habitable zone of the star – is an excellent target for this research goal,” she tells New Atlas.


Transit authorities

One of the inherent difficulties in exoplanet research is the blinding light that comes from the parent star. This makes it impossible to directly image the circling exoplanets. Instead, they are detected through what is known in astronomy circles as transiting, where orbiting planets create dips in the star’s light as they pass in front, revealing their presence to exoplanet hunters here on Earth. TRAPPIST-1, the system’s parent star, is dim and small (around the size of Jupiter), but not dim enough to directly image its planetary system.  


“The planets are too close to their star to resolve even with a large telescope like JWST, so we’ll still be relying on the transit method,” Burgasser says. “However, JWST will allow us to search not just for starlight blocked by the planets, but starlight that filters through their atmospheres, which will allow us to measure the temperatures and chemical compositions of those atmospheres in more detail, necessary to search for life.”

This technique is called transit spectroscopy and will be the main approach used to study the atmospheres of the TRAPPIST-1 system through the JWST. Deck explained to us how it works.

“When a planet passes in front of a star, it blocks light from that star,” she says. “A bigger planet will block more light. If a planet has an atmosphere, that atmosphere extends the size of the planet past the size of the rocky core, and so planets with atmospheres block additional light, compared with those with the same size rocky core, without an atmosphere.

“The key point is that the atmosphere only blocks light of certain colors, or wavelengths, which correspond to particular wavelengths of light that excite particular molecules in the atmosphere. Effectively, JWST will look at a host star with different filters on, isolating particular colors of light from the star. When the transit happens, the amount of light blocked by the planet will be different in each of the filters, depending on which molecules are present in the atmosphere and on other characteristics of the atmosphere.”


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